1. Field of the Invention
The present invention relates to a developer for developing an electrostatic latent image for use in electrophotography, electrostatic printing, and the like. The invention also relates to a developer (toner and carrier) for use in a direct recording-apparatus in which toner is forced to fly from a toner supporting-member directly onto a recording member so that toner images are formed.
2. Description of the Related Art
Developers for developing electrostatic latent images for use in electrophotography, electrostatic printing, and the like have been produced by a kneading-pulverizing method or by wet processes such as a suspension polymerization method. Further, it has been known to surface-modify developer particles by various means (mechanical impact force, heat, or the like) after preparation of the developer in order to improve the properties of particles produced by the above method. Among those methods, a process of instantaneous heat treatment for surface modification has been known. For example, Japanese Patent Application Laid-Open Nos. Hei 6-317928 to Hei 6-317933 disclose about an instantaneous heat-treatment of a magnetic toner. In these prior art publications, there is a statement that if the temperature for treatment is set high, particle agglomeration may occur, and that in order to cope with such a problem it is desirable to use a binder resin having a melting viscosity of 1.times.10.sup.4 -5.times.10.sup.5 (poise) at 135.degree. C. and 3.times.10.sup.3 -3.times.10.sup.5 (poise) at 145.degree. C. However, with such resin properties shown in these publications, it is impracticable to use such a resin in a low temperature fixing/high speed system. This system is increasingly required in recent years. Further, such a resin cannot satisfy resin properties required of the resin for use in a full color system and lacks general purpose.
Japanese Patent Application Laid-Open No. Hei 4-226476 discloses a toner (non-magnetic toner) in which after resin particles and a developer composition (including carbon black, quaternary ammonium salt having a mean particle size of several .mu.m, and polypropylene etc.) are mixed together, the mixture is instantaneously heat-treated for melting and adherence. In such a method, however, agglomeration and coalescence (bonding) of particles are unavoidable.
In a conventional method it may have been possible to modify the surface conditions to enhance the performance quality of the developer. Recently, however, in copying apparatuses and printers, an image quality of higher level has been required more than ever. In order to meet such a requirement it is necessary to achieve improvement on the machine side with respect to copying apparatuses, developing devices etc. In addition, it is essential to achieve functional improvement of developers. In order to improve the function of the developer, it is necessary to control variations in particle configuration of individual developer particles and to enhance characteristic uniformity of the surface of individual particles. In this sense, the prior art method has not reached the characteristic level required for above mentioned purposes. Further property-improvement has been demanded.